1. Field of the Invention
This invention relates to a document processing apparatus for adjusting document data so as to make a document easily visible to people with color blindness.
2. Description of the Related Art
People use various colors to classify or represent information for the purpose of easily understanding the information and enhancing visibility. For example, a traffic signal uses three colors of red, yellow, and blue to control traffic. In addition to such public departments, graphs, etc., as materials used in a company are colored by item for easy understanding using a color printer or a large number of colors are also used for background images of slides created using presentation software.
Such use of colors provides advantages for persons with normal color vision to easily understand information definitely. However, such use of colors does not necessarily lead to easy understanding for people with colorblindness. For example, for a person with color blindness who is hard to distinguish between red and green, a graph colored properly in red and green becomes hard to see.
According to physiological and medical studies concerning the color vision of a human being, it is known that there are three types of color blindness P, D, and T. The state of the color blindness can be better understood using the color component space represented by CIE XYZ color system xy chromaticity diagram defined from the viewpoint of physiological optics. That is, when lines (called confusion color lines or confusion color loci) are drawn radially from one point on the xy chromaticity diagram (which will be hereinafter called intersection point for convenience of the later description), if the colors on the same line (called confusion colors) have the same lightness, it is made impossible for persons with each type of color blindness to distinguish between the colors. The intersection point position varies depending on the type of color blindness (P, D, or T); the intersection point for P and that for D are positioned in the lower right part on the CIE chromaticity diagram and the intersection point for T is positioned in the lower left part. It is also known that defective color vision of T occurs comparatively rarely.
Then, if confusion colors are contiguous, an art is available for adjusting the luminance signal of the boundary between the confusion colors for making the boundary conspicuous, as described in JP-A-2002-44678.